CONCORD _ Rockingham Park’s president told state lawmakers Wednesday charitable gaming will suffer if casinos open in Massachusetts and the Granite State, but he stressed that under the New Hampshire gambling bill, the new casino would replace any lost revenue to charities.

“When casinos in Massachusetts open, they will have an impact on the charitable gaming in New Hampshire, particularly from Manchester south,” Edward Callahan said at meeting of a gambling subcommittee investigating the “community impact” of opening a casino in the Granite State.

Callaghan, in addition to being president of Rockingham Venture, the owners and operator of Rockingham Park, is the sole owner of Rockingham Gaming LLC, the licensed operator for charitable games of chance at Rockingham and Seabrook parks.Callahan said he anticipates that gambling in Massachusetts will reduce the charitable business in southern New Hampshire by 20 percent.

“The addition of a New Hampshire casino on the southern New Hampshire border would have a similar impact on charitable gaming from Concord south,” Callahan said.“The difference with a Massachusetts casino and no New Hampshire casino would be the revenue guarantees provided for in Senate Bill 152,” the casino gambling bill for New Hampshire, said Callahan.

“Massachusetts will open up to four gaming facilities, with the Boston region and the western Massachusetts region providing the greatest impact on New Hampshire. This impact will cover a region in New Hampshire which provides up to 80 percent of the charitable gaming revenue.”

But he said that if SB 152 passes, “the revenue guarantees provided could keep all the New Hampshire charities who conduct charitable games of chance, bingo and Lucky 7’s with a revenue stream equal to that in 2012.”

Callahan noted that some charitable gaming operators fear that with a casino in the state, they would be forced to close their doors and as a result not qualify for the revenue guarantees provided in the casino bill.

But he said that since the licensed casino facility would be required to provide charitable gaming space, “with the anticipated number of casino visits in the 4 million to 5 million range, I believe the revenue generated in that particular (charitable gaming) room would be three to four times greater than the revenue currently generated in the largest room in the state.”

He said that if the operator of the casino facility and the charitable game operator provided dates to charities who were no longer invited to other facilities, “they would simply need to operate one day per year to qualify and in most cases would generate more revenue at that facility on one day that they currently do in 10.”

He also suggested that a group of charities can join together and hire an operator to provide a facility for them, “as one day per year would allow them to continue to qualify” and “every currently operating charity would be able to continue to participate.”

Callahan explained that if Rockingham were to be licensed to operate a casino, the casino floor would be divided by “attractive fencing” between the full-fledged casino and the charitable gaming casino.

Anyone between ages 18 and 21 would be directed to the charitable gaming casino, he said.